Centrifuges of the above described general type are known, for example, from the foreign Patent Publications DE 22 07 663 C3, DE 25 50 496 A1, DE 90 04 952 U1 or EP 0 487 780 B1. In the conventional centrifuges, the sugar massecuite is firstly introduced into the central region of the centrifuge and is then guided by means of a distributing pot or in another manner into the narrower inner region of the perforated basket. In the course of this process, the massecuite is accelerated to a peripheral speed in the distributor or in an accelerating bell or a foreworker drum, and is then spun off outwardly.
The particles then reach the sugar narrow inner region, usually located at the bottom, of the perforated basket which widens conically upwards, and then "drift" slowly up the inner wall until they reach the throwing-off edge. Once they reach this edge they are spun off outwardly.
There are three variations of the above process in the state of the art. The centrifuges produce either, dissolved sugar, mingled sugar, or dry sugar, and are respectively operated as dissolving, magmatizing or dry centrifuges. In the first case, the separated and purified sugar crystals are re-dissolved in various ways. In the second case, a magmatizing process is additionally incorporated in which the crystals remain but the surrounding syrup coating is partially dissolved and is ultimately exchanged for a purer syrup coating. In the third case, the dry sugar crystals are discharged downwardly and conveyed away by means of a transporting device.
The three modes of operation each require different centrifuges, and it is not possible to take one centrifuge designed for one of these purposes and use it freely for another purpose. This means restricted flexibility for the user and disadvantages in terms of stock for the manufacturer.
It has therefore already been proposed, for example in German Patent Publications DE 90 04 952 U1 and DE 29 10 625 A1, to arrange two centrifuges one above another, for example one operating as a magmatizing centrifuge and the other as a dissolving centrifuge, in order to have both available in one constructional unit in a space-saving manner. This is advantageous but costly.
In contrast, to the above state of the art the object of the invention is to propose a continuously operating centrifuge for spinning sugar massecuite, which is suitable for a plurality of applications, i.e. which can be operated in more than one of the above described modes.
The object is achieved by the invention having the above mentioned perferated conical basket and further processing device, in that the further processing device has a collecting channel, preferably removable, with at least one discharge nozzle at the base, thereof and in that an overflow nozzle may selectively by installed at the discharge nozzle.
The special construction of the collecting channel allows the centrifuge of the invention to be used both as a magmatizing centrifuge and a dissolving centrifuge. Furthermore, the present centrifuge can be used as a drying centrifuge by simply removing the collecting channel.
For use as a dissolving centrifuge, the outlet of the collecting channel is blocked by putting on or installing the overflow nozzle. The dissolving medium, i.e. water and/or thin juice, and the sugar crystals that have already formed are collected and dissolved in the collecting channel. A mass of clarifying liquor is formed in the collecting channel because of the overflow nozzle, which has a dam effect that causes the liquid to pool-up to a certain level before it can drain through the outlet. Thus, a residence time is produced for subsequent dissolving.
Undissolved crystals will sink to the base of the collecting channel.
In order to also dissolve residual crystals as far as possible, i.e. during use as a dissolving centrifuge, it is preferred for at least one steam conduit to be arranged in the base region of the collecting channel inside the clarifying mass and for steam to be fed in. The steam conduit(s) can be removable so that they do not become encrusted during other modes of use.
The level of liquid rising above the overflow nozzle will then flow through the overflow nozzle into the discharge nozzle, from which the liquid can discharged and collected.
It is also possible to regulate the level of the mass of clarifying liquor by using different overflow nozzle heights. The overflow nozzle is preferably adjustable in height in a step-free manner, or nozzles of different heights can be used.
The dissolving centrifuge known, for example, from German Patent Publication DE 25 50 496 A1 also collects the spun-off sugar crystals, but not in a collecting channel. It could not be used as a magmatizing centrifuge as the viscous magma would clog up all the parts immediately.
In order for the centrifuge of the invention to function as a magmatizing centrifuge, the overflow nozzle is removed. The affining magma, which flows out very slowly in comparison to clarifying liquor, is then directly guided away without any danger of clogging. The magmatizing medium is preferably conveyed via an outer ring conduit to a rebounding surface which is formed by or projects from the wall of the collecting channel remote from the perforated basket. A layer of the magmatizing medium thus spreads over the rebounding surface and the spun-off sugar crystals penetrate the layer.
The further processing equipment preferably surrounds the perforated basket in an annular way. This ensures that further processing of the sugar crystals is uniform in all applications.
Provision is also preferably made for a supply device, particularly a ring conduit, to supply the dissolving medium in the region of the throwing-off edge of the perforated basket especially for operation in the dissolving mode. The said ring conduit extends at a relatively small distance above the throwing-off edge and sprays the dissolving medium or delivers it in another way to the sugar crystals which are spun off in this region. The rotating drum of the perforated basket causes the solvent to be strongly agitated and it is thrown together with the sugar crystals tangentially away from the perforated basket and over the collecting channel towards a rebounding surface positioned behind the channel. The agitation promotes the dissolving effect even during the throwing process, and brings about uniform distribution of the sugar crystals and the dissolving medium. The sugar crystals and dissolving medium then slide off the rebounding surface down into the collecting channel, which has already been filled with dissolving medium and sugar crystals dissolved therein during operation of the apparatus. During the static residence time, the sugar crystals dissolve further inside the said channel and the clarifying liquor then flows through the overflow nozzle into the discharge nozzle.
It is possible to allow the collecting channel to extend in an annular form as a continuous channel around the perforated basket. However, it is preferred for the further processing device to have a plurality of collecting channels which each have at least one discharge nozzle at the base thereof, whereby provison is made for overflow nozzles of the discharge nozzles. This allows more specific access and more precise determination of the respective products in terms of quantity.
It is particularly preferable for oblique surfaces to be arranged between each two adjacent collecting channels, ensuring that particles lying thereon will slip into the neighbouring collecting channel.
In case that in many applications stray particles form above the further processing device. It should also be taken into account that the spun-off sugar crystals and adhering syrup residue are spun off tangentially, not radially, and have corresponding displacement components.
It is possible to group the plurality of collecting channels in succession in the peripheral direction around the perforated basket. However, it is particularly preferable for the further processing device, surrounding the perforated basket in an annular form, to have a serrated profile, i.e. a bottom made up of stepped, sloped bottom sections, when seen in a section at a constant distance from the axis of the perforated basket, the discharge nozzles being arranged at the deepest points of the profile.
This means that the collecting channels, when seen from the interior of the perforated basket, are each arranged next to one another like basins, each at the same distance from the axis of the perforated basket, and each separated from one another or connected to one another by oblique surfaces.
The collecting channels and the oblique surfaces positioned therebetween (arranged with even their highest points below the throwing-off edge of the perforated basket) are closed towards the outside by a rebounding wall .